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// Copyright (c) 2015 Baidu, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Author: Ge,Jun (gejun@baidu.com)
// Date: Tue Jul 28 18:15:57 CST 2015
#ifndef BVAR_DETAIL_SAMPLER_H
#define BVAR_DETAIL_SAMPLER_H
#include "butil/containers/linked_list.h"// LinkNode
#include "butil/scoped_lock.h" // BAIDU_SCOPED_LOCK
#include "butil/logging.h" // LOG()
#include "butil/containers/bounded_queue.h"// BoundedQueue
#include "butil/type_traits.h" // is_same
#include "butil/time.h" // gettimeofday_us
#include "butil/class_name.h"
namespace bvar {
namespace detail {
template <typename T>
struct Sample {
T data;
int64_t time_us;
Sample() : data(), time_us(0) {}
Sample(const T& data2, int64_t time2) : data(data2), time_us(time2) {}
};
// The base class for all samplers whose take_sample() are called periodically.
class Sampler : public butil::LinkNode<Sampler> {
public:
Sampler();
// This function will be called every second(approximately) in a
// dedicated thread if schedule() is called.
virtual void take_sample() = 0;
// Register this sampler globally so that take_sample() will be called
// periodically.
void schedule();
// Call this function instead of delete to destroy the sampler. Deletion
// of the sampler may be delayed for seconds.
void destroy();
protected:
virtual ~Sampler();
friend class SamplerCollector;
bool _used;
// Sync destroy() and take_sample().
butil::Mutex _mutex;
};
// Representing a non-existing operator so that we can test
// is_same<Op, VoidOp>::value to write code for different branches.
// The false branch should be removed by compiler at compile-time.
struct VoidOp {
template <typename T>
T operator()(const T&, const T&) const {
CHECK(false) << "This function should never be called, abort";
abort();
}
};
// The sampler for reducer-alike variables.
// The R should have following methods:
// - T reset();
// - T get_value();
// - Op op();
// - InvOp inv_op();
template <typename R, typename T, typename Op, typename InvOp>
class ReducerSampler : public Sampler {
public:
static const time_t MAX_SECONDS_LIMIT = 3600;
explicit ReducerSampler(R* reducer)
: _reducer(reducer)
, _window_size(1) {
// Invoked take_sample at begining so the value of the first second
// would not be ignored
take_sample();
}
~ReducerSampler() {}
void take_sample() {
// Make _q ready.
// If _window_size is larger than what _q can hold, e.g. a larger
// Window<> is created after running of sampler, make _q larger.
if ((size_t)_window_size + 1 > _q.capacity()) {
const size_t new_cap =
std::max(_q.capacity() * 2, (size_t)_window_size + 1);
const size_t memsize = sizeof(Sample<T>) * new_cap;
void* mem = malloc(memsize);
if (NULL == mem) {
return;
}
butil::BoundedQueue<Sample<T> > new_q(
mem, memsize, butil::OWNS_STORAGE);
Sample<T> tmp;
while (_q.pop(&tmp)) {
new_q.push(tmp);
}
new_q.swap(_q);
}
Sample<T> latest;
if (butil::is_same<InvOp, VoidOp>::value) {
// The operator can't be inversed.
// We reset the reducer and save the result as a sample.
// Suming up samples gives the result within a window.
// In this case, get_value() of _reducer gives wrong answer and
// should not be called.
latest.data = _reducer->reset();
} else {
// The operator can be inversed.
// We save the result as a sample.
// Inversed operation between latest and oldest sample within a
// window gives result.
// get_value() of _reducer can still be called.
latest.data = _reducer->get_value();
}
latest.time_us = butil::gettimeofday_us();
_q.elim_push(latest);
}
bool get_value(time_t window_size, Sample<T>* result) {
if (window_size <= 0) {
LOG(FATAL) << "Invalid window_size=" << window_size;
return false;
}
BAIDU_SCOPED_LOCK(_mutex);
if (_q.size() <= 1UL) {
// We need more samples to get reasonable result.
return false;
}
Sample<T>* oldest = _q.bottom(window_size);
if (NULL == oldest) {
oldest = _q.top();
}
Sample<T>* latest = _q.bottom();
DCHECK(latest != oldest);
if (butil::is_same<InvOp, VoidOp>::value) {
// No inverse op. Sum up all samples within the window.
result->data = latest->data;
for (int i = 1; true; ++i) {
Sample<T>* e = _q.bottom(i);
if (e == oldest) {
break;
}
_reducer->op()(result->data, e->data);
}
} else {
// Diff the latest and oldest sample within the window.
result->data = latest->data;
_reducer->inv_op()(result->data, oldest->data);
}
result->time_us = latest->time_us - oldest->time_us;
return true;
}
// Change the time window which can only go larger.
int set_window_size(time_t window_size) {
if (window_size <= 0 || window_size > MAX_SECONDS_LIMIT) {
LOG(ERROR) << "Invalid window_size=" << window_size;
return -1;
}
BAIDU_SCOPED_LOCK(_mutex);
if (window_size > _window_size) {
_window_size = window_size;
}
return 0;
}
void get_samples(std::vector<T> *samples, time_t window_size) {
if (window_size <= 0) {
LOG(FATAL) << "Invalid window_size=" << window_size;
return;
}
BAIDU_SCOPED_LOCK(_mutex);
if (_q.size() <= 1) {
// We need more samples to get reasonable result.
return;
}
Sample<T>* oldest = _q.bottom(window_size);
if (NULL == oldest) {
oldest = _q.top();
}
for (int i = 1; true; ++i) {
Sample<T>* e = _q.bottom(i);
if (e == oldest) {
break;
}
samples->push_back(e->data);
}
}
private:
R* _reducer;
time_t _window_size;
butil::BoundedQueue<Sample<T> > _q;
};
} // namespace detail
} // namespace bvar
#endif // BVAR_DETAIL_SAMPLER_H